Dr. Harlan Krumholz (@HMKYale) is a cardiologist and the Harold H. Hines, Jr. Professor of Medicine and Epidemiology and Public Health at Yale University School of Medicine.

Drinks and foods marketed to help us maintain weight may have been helping us to gain it, says WSJ Health Expert Harlan Krumholz. Photo: iStock Photo

I used to pound down diet drinks. Low-calorie had to be good, right? It was an invitation to enjoy as much as I wanted, guilt-free. Diet soda was a source of caffeine, and a companion.

And this was all consistent with my identity as a cardiologist. I am very interested in the prevention of heart disease—for my patients for the public, and for myself. So while I never saw diet soda as a health drink, I felt it helped keep my weight under control.

New research, however, has raised the very real possibility that the non-sugar sweeteners that put the “diet” in diet drinks (and many low-calorie foods), may have been conspiring against me.

Rather than help me maintain a healthy weight, they may have been predisposing me to weight gain and metabolic abnormalities. This research is suggesting that drinks and foods using artificial sweeteners like aspartame may be doing exactly what we thought they should be preventing. At the very least, they do not seem to help people keep weight off.

The study in the Canadian Medical Association Journal searched the literature for randomly controlled studies involving non-nutritive sweeteners. They found a mere seven trials, with a total of only 1,003 people, that evaluated consumption of the substances for more than six months.

The bottom line was that they generally failed to find that sweeteners helped people lose weight. Since most people use sweeteners for the purpose of controlling or losing weight, if they were considered drugs instead of a food substance they would be deemed ineffective based on the best evidence available.

The researchers also looked at 30 observational studies, those that did not involve changing people’s diets, but merely cataloging the diet and determining changes over time. They found that people who consumed these sweeteners were more likely to have increases in weight and waistline, and a higher incidence of obesity, hypertension, metabolic syndrome, Type 2 diabetes and cardiovascular events.

One could argue that people who consume diet foods may have already been predisposed to gaining weight and to these other conditions. Many discount these nonexperimental studies—I know I have done so for years. But now I am taking another look as studies are starting to indicate that diet sweeteners could be hurting, instead of helping weight-loss efforts.

Colleagues at my institution argued in 2015 that such sweeteners are far from inert. They showed an impact on hormone secretion, cognitive processes and gut microbiota—and concluded that all of these effects could counter weight control intentions. Another recent peer-reviewed publication presented animal studies that are disturbing. The effects of these sweeteners seem to vary based on the type, dose and timing. What was clear is that these substances again were linked to weight gain and metabolic disturbances.

A study of one substance called sucralose found that its sweetness affected a different part of the brain than sugar. The point was that even though people perceive the sweetness of sugar and sucralose similarly, the brain sees them differently, which may have implications for hunger and reward.

It is reasonable to ask why these substances were not evaluated as drugs in the first place. Millions of people are exposed to them every day, and yet their long-term effect is uncertain. Could they be actually causing the health problems they were intended to prevent? I don’t know the answer at this point, but it seems to me that the burden of proof is on the manufacturers to show benefit and demonstrate safety through clinical trials.

Meanwhile, I’ve stopped my daily habit of diet drinks and I am slowly removing these substances from the rest of my diet (given their ubiquity, that is not easy). If, in the end, we discover that large-scale consumption of diet drinks and foods helped fuel the obesity epidemic, it would be more than ironic. It would be tragic.